1. Field of the Invention
The present invention relates to a surface acoustic wave apparatus for extracting a convolution signal of two surface acoustic wave signals, utilizing the physical nonlinear effect, and to a spread spectrum signal receiver and a communication system using it.
2. Related Background Art
Surface acoustic wave convolvers for extracting a convolution signal of two surface acoustic wave signals are increasing its significance as a key device in performing spread spectrum communication these years and are actively being researched.
FIG. 1 is a schematic drawing to show a conventional surface acoustic wave convolver device. In the drawing, numeral 111 designates a piezo-electric substrate of Y-cut (Z-propagation) lithium niobate or the like, and numerals 112, 113 interdigital input electrodes formed on the surface of the piezo-electric substrate 111. Numeral 114 denotes an output electrode formed on the surface of the piezo-electric substrate 111.
When high-frequency signals of angular frequency .omega. are input into the interdigital input electrodes or transducers (IDTs) 112, 113 in the surface acoustic wave convolver device, the two signals propagate on the surface and inside the piezo-electric substrate to be confined in the output electrode 114 and, for example by the nonlinear effect of the piezo-electric substrate, a signal of angular frequency 2.omega. can be obtained from an output pad of the output electrode 114.
These electrodes are made of a conductive material such as aluminum, and are formed directly on the surface of the piezo-electric substrate 111 normally by the photolithography technology. This mechanism of convolution is described in detail, for example, in Shibayama, "Applications of surface acoustic wave," Television, 30, 457 (1976). The surface acoustic wave convolver device is mounted on a metal or ceramic package base with a space secured above a propagation path of surface acoustic wave and, after bonding with wires, the package is airtightly sealed by a metal cap in order to assure reliability.
The package housing the surface acoustic wave device is placed together with convolver peripheral circuits including a convolver input-output matching circuit etc., and spread spectrum communication transmission-reception circuits on a printed-wiring board of glass/epoxy or the like, and the resultant is applied to surface acoustic wave convolver apparatus or spread spectrum communication apparatus.
However, because the conventional surface acoustic wave convolver device needs to be airtightly sealed as housed in the metal or ceramic package, there are disadvantages that the package size becomes larger and that the cost becomes higher.
Particularly, the element length of the surface acoustic wave convolver device is longer than those of the other surface acoustic wave devices such as a filter in which an output electrode is positioned as opposed to an input electrode, because the long output electrode exists as opposed to each of the input electrodes at the both ends.
Further, if a convolver with a large signal processing time length is needed, the element length becomes longer in proportion to the signal processing time length and a package larger by that degree becomes necessary, which would result in disadvantages of increasing the size and the cost of the entire surface acoustic wave apparatus.
If output signals are taken out from plural positions on the output electrode of convolver, it is necessary to form a tournament-shaped output synthesis pattern in the package or on the printed-wiring board, which would result in a disadvantage that the size of the spread spectrum communication apparatus including the package and the printed-wiring board becomes larger.
A conventionally known technique for sealing the surface acoustic wave filter is the technique in which a recess is formed in a multilayer wiring substrate and the surface acoustic wave filter is housed in the recess to be sealed therein, as disclosed in Japanese Laid-open Patent Application No. 1-273390. The present invention is the one having been achieved by applying the above technique to the convolver devices inherently involving the problem that the element length becomes longer than those of ordinary surface acoustic wave filters.
An object of the present invention is to provide a surface acoustic wave apparatus using a convolver device, a spread spectrum communication apparatus, and a system using it, as decreasing the size and the cost of the surface acoustic wave apparatus associated with the package for convolver device and decreasing the size and cost of the spread spectrum communication apparatus using it.
A further object of the present invention is to decrease the size and cost of the surface acoustic wave apparatus for extracting convolution signals from plural positions of the output electrode in order to take a convolution output out from convolver without a phase difference.